Selective call communication (paging) systems typically comprise a radio frequency transmitter/encoder (base station) that is accessed via a link to the Public Switched Telephone Network (PSTN) and a radio receiver (e.g., a selective call receiver or the like) that has at least one unique call address associated therewith. Operationally, the selective call receiver receives and decodes information transmitted from the base station, the information including an address and possibly a data or voice message. When the selective call receiver detects its address, it may alert a user and present message information received.
To implement messaging capability in a paging system, the address and message information referred to are encoded and subsequently transmitted using a protocol such as GSC (Motorola's Golay Sequential Code) or POCSAG (a code from Great Britain's Post Office Code Standardisation Advisory Group). These protocols are adapted to reliably communicate messages to at least one selective call receiver and are well known to one of ordinary skill in the art of paging systems. A typical selective call message may consist of an address signal if the message is a tone only message, or an address signal and a data packet if the message is a data message.
Present selective call receivers operate almost exclusively in a standalone fashion, that is, received messages can only be presented by the receiver's display. Some conventional selective call receivers include a serial data interface for communicating a single received message to an alternate presentation device such as a printer or possibly an electronic advertising sign. Presently, state of the art selective call receiver serial communication systems use a three wire serial interface operating at data rates from 300 to 9600 baud. This serial architecture inherently limits the data bandwidth (speed and information content) between the receiver and a data device. Moreover, since the three wire interface has only transmit data, receive data, and ground connections, any control signals must be encoded as serial data symbols, further slowing response time and limiting the data bandwidth. Lastly, since these interfaces are proprietary in nature, that is, there is no standard for signal levels, data rates, or protocols, data interchange between devices of different manufacturers is all but impossible because of a lack of convention.
Even if a parallel or memory bus scheme is adopted for communicating data between the selective call receiver and the data device, there is still a problem when this is implemented using the PCMCIA memory-only interface standard. By definition, PCMCIA memory-only interface peripherals don't include any means for generating a signal for notifying the data device of a need for service. Moreover, PCMCIA memory-only interface peripherals don't have a native mode that allows for the execution of configuration or service commands useful to interrogate data of a dynamic nature stored within the peripheral. This severe shortcoming limits the usefulness of a memory-only PCMCIA interface peripheral to situations where relatively static data is needed, e.g., as a ROM card or the like.
A final consideration is that the messaging information received by a memory-only PCMCIA interface peripheral may be proprietary in nature. In this case, one may simply remove the memory-only PCMCIA interface peripheral from a first host and insert it into a second host, then read the messaging information. This possibility would allow an unauthorized person to "steal" one's private messages without their knowledge. Similarly, if the memory-only PCMCIA interface peripheral is left in the first host and the owner has left the area, leaving the host unprotected, the unauthorized user may read the authorized user's confidential messaging information.
Consequently, what is needed is a standardized communication interface for state of the art selective call receiver systems that provides a capability to effectively communicate received information between a microcomputer or the like. Additionally, the memory-only PCMCIA interface peripheral should be able to either manually or automatically protect received messages from unauthorized access.